How deep is my main sewer line?

Author: Ms. Madilyn Weimann  |  Last update: Wednesday, August 27, 2025

The sewer pipe(s) that leave your house and flushes everything into the sewer main can be anywhere from four-feet to ten-feet under ground depending on if you have a basement or your house is built on a slab. Some sewer pipes are installed deeper than that.

How do you find out how deep your sewer line is?

Contact Your City's Engineering Department

You could also contact someone in your city's zoning office. In most cases, you'll be able to know where your sewer line is and how deep it's buried. Depending on the city you reside in, you could even get a copy of various helpful documents, like your property map.

How far down is the main sewer line?

The main sewer pipes run right down the middle of the roadway. They're normally about ten feet below the surface, although they might be a lot deeper. Once you know the depth and location of the main sewer, you can calculate the slope required for your sewage to flow freely through the pipe and into the main sewer.

How deep does a residential sewer line have to be?

Residential sewer line pipe depths range from as shallow as 18 to 30 inches in depth or 5 to 6 feet deep. However, in colder climates where freezes occur, you often see sewer line depths ranging from 4 to 8 feet deep. This ensures the pipes are below the freeze line.

How deep to dig for a 4 inch drain pipe?

The trench should be about 18 inches deep and 9 to 12 inches wide.

Plumbing Slope Rule and Why it is CRITICAL

How much fall should a 4 sewer line have?

A 4-inch horizontal drainage pipe's minimum slope is 1% to 2% (or 1/8 inch to 1/4 inch per foot). The pipe should slope downward 1/8 inch to 1/4 inch per foot for drainage and to prevent clogs.

How do I know where my sewer line runs?

Dial 811

Probably the most convenient method, you can dial 811 in the United States. This national hotline connects you to your local utility company, allowing you to request that utility professionals come to your property and mark the location of various underground utilities, including your sewer lines.

How deep should a sewer line be under a slab?

Believe it or not, plumbing pipes under a slab house foundation is typically 12 to 24 inches deep. The pipes are installed into trenches and then buried before the rebar, wire mesh, and concrete slab are poured.

How deep is a sewer cleanout?

The sewer cleanout is capped off with a cleanout cap where the pipe is open above ground. Whether your sewer line is 8' deep or 3' deep it doesn't matter. The section of pipe that is extending the sewer opening above ground will give access to your sewer line without having to dig up your sewer line.

How many main sewer lines does a house have?

All the drains in your home lead to one main sewer line, which goes into the municipal system or to your septic tank system.

How deep are septic tanks buried?

The septic tank is often buried about six feet deep and ten feet away from the building.

Does the main sewer line always have water in it?

The second answer is NO: If you notice that drains are overflowing or making a gurgling noise or even sucking the water seal dry it would most likely point towards a fault in the drainage system.

What size is my main sewer line?

The most common sewer pipe size is four inches in diameter, but there are also six and eight-inch pipes available, which are also sometimes referred to as concrete storm sewer pipe sizes.

How much does it cost to fix a clogged sewer line?

You will likely pay around $350 to $650 to have a plumber unclog a main sewer line unless you have complications like serious damage to the line.

How to unclog main sewer line?

Your step-by-step guide: How to clear a main sewer line clog
  1. Step 1: Loosen the cap on the drain pipe. ...
  2. Step 2: Open the cap and let the buildup drain out. ...
  3. Step 3: Feed the auger cable into the drain pipe. ...
  4. Step 4: Run the auger until the clog is clear—and beyond. ...
  5. Step 5: Hose down the pipe and auger cable.

How deep should a sewage drain be?

In general, pipe runs made of blue MDPE should be buried at least 750mm below finished ground level. In addition, they should be positioned 350mm from other pipes and utilities. Alternatively, they can be buried in a trench that is at least 300mm wide and as deep as the pipe itself.

Does sewer pipe go under footing?

Yes, your main water line can definitely (and usually does) run underneath the footing. Your sewer line also usually needs to run under the footings to allow for downward slope from any plumbing drains in the basement to the sewer main.

What does the main sewer line look like?

You may spot a 3 to 4-inch diameter pipe peeking out of the slab floor of the basement. The sewer drain pipe could be made of plastic or cast iron; it might be copper or brass in rare cases. The stub-out will have a screw-in plug coupled with a square-head lug on it, representing your access to the main drain.

How do I test my main sewer line?

Test Balls for Drainage Lines

To start the process, make sure your main line sewer cleanout is clear of debris and liquid. Next, insert the test ball and inflate it so that it blocks the main line. Fill the sewer system with water and observe the water level for 15-20 minutes.

Do all houses have a sewer cleanout?

A lot of people think they don't have sewer cleanouts. But as I said, pretty much all homes do these days. It's more likely that your sewer cleanout is buried, often in a flower bed area. People cover up the cleanout because they think it's an eyesore.

What is the proper drop for a sewer line?

The general rule is 1/4″ of pitch per foot of run. However, some other issues do come into play. An extreme amount of pitch can cause the wastewater inside the drain to flow extremely fast.

How many toilets can be on a 4 inch drain?

4″ waste line can support 90 DFU's, Toilets can be 3–4 DFU's depending on how many gallons per flush. So, 22 toilets if they use a lot of water.

Can a sewer line have a 45 degree angle?

Re: Are 45 degree fittings allowed in horizontal drain pipe? To answer your question, yes they are allowed, but only in a horizontal configuration. You cannot use them to change elevation.

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